The invention relates to suspensions for vehicles, for cushioning shocks on an axle assembly caused by irregularities in the track or ground before they can be transmitted to the vehicle frame. It was developed primarily for underground mine haulage locomotives used in low height mines where there is insufficient head room to accommodate the full vertical movement of the vehicle frame if conventional journal box wheel suspensions were used. It will be apparent as the description proceeds that the improved suspension may usefully be applied to other railway and non-railway type vehicles, to obtain maximum cushioning where only limited vertical movement of the frame is permissible because of low head room or for other reasons.
The problem of moving heavy loads over bad road beds under a low ceiling is perhaps unique to underground mines, and to coal mines in particular. Most mine track undulates up and down, and sidewise, because it is not economical to lay it with straight line, above ground precision on a deep, stable road bed. And, once installed, the track conditions often worsen due to irregular heaving of the mine bottom and constant back and forth movements of heavy mine cars and locomotives.
Attempts have been made to develop vehicles for use in thin seam coal mining, in which there is little or no relative vertical movement between the wheels and the body. For example, about 20 years ago, considerable work was done by mining machine manufacturers attempting to develop a shuttle car with wheels solidly connected to a flexible steel body. The body was supposed to flex as it moved across uneven bottom. Unfortunately, the body strength required to hold and transport several tons of coal was not compatible with the required flexibility so the bodies were constantly breaking up. After much money was spent, the flexible body idea was abandoned.
Similar attempts to mount the wheels rigidly on the bodies of mine haulage locomotives were unsuccessful. On rough track, some of the wheels would always be out of engagement with the rails, allowing the locomotive to derail easily.
More recently, light weight, self propelled personnel cars have been developed to transport men and supplies in underground mines. In one such car, for low height mines, each axle assembly was mounted between a pair of trunnions for rocking movement against springs, about a central, longitudinal axis. The trunnions were pivotally journaled in swivel blocks which were connected solidly to the frame, fore and aft of each axle assembly. Although there was no relative vertical movement between the frame and the axle assemblies, some cushioning was provided for personnel by rocking the axle assembly upward against the springs. This was quite successful in preventing derailment while limiting vertical movement of the frame and reducing to an appreciable extent the transfer of shocks from the wheels to the frame. However, on long trips, the ride was rough and uncomfortable.
The above mentioned personnel cars were subsequently improved by the development of a rocking hinge type suspension. This was similar to the suspension described in the above paragraph except that one of the trunnion swivel blocks was hinged on the frame while the axle assembly and the opposite swivel block swung upward against the springs. This construction is shown in U.S. Pat. No. 4,085,682 issued Apr. 25, 1978 to Robert C. Nelson et al. This represented a substantial improvement in the suspension for personnel cars. The axle assembly rocked about a longitudinal axis through the trunnions as previously. In addition, the axle assembly tilted up and down, with the springs absorbing shocks from both tilting and rocking movements. Rider comfort was improved, especially on long trips.
In the above described improved personnel cars, the vertically movable swivel block at the tiltable end of the axle assembly has been slideably guided for up and down movement between a pair of transversely spaced, vertical guide plates. While this particular construction is quite satisfactory for relatively light duty personnel carriers, it lacks the ruggedness and friction-free precision needed to apply the rocking hinge suspension principle to heavy duty mine haulage locomotives.